Structural studies of the Tudor domain from the Bombyx homolog of Drosophila PAPI: Implication to piRNA biogenesis

PIWI proteins and their associated PIWI-interacting RNAs (piRNAs) play crucial roles in proper gametogenesis in animal gonads. Partner of PIWIs (PAPI) is one of the important piRNA biogenesis factors. PAPI contains a Tudor domain and tandem KH domains. The tudor domain specifically recognizes symmetrical-dimethylarginines (sDMAs) on PIWI proteins. BmPAPI, a Bombyx mori homolog of PAPI, is localized at the outer membrane of mitochondria and supports exonucleolytic trimming of piRNA precursors to form mature 3-prime-end of piRNAs. To understand the structural basis of piRNA processing by BmPAPI, we present crystal structures of the apo- and sDMA-liganded Tudor domain of BmPAPI.